1. Field of the Invention
The present invention relates to an insulating sealing resin for an alkaline battery, and more particularly to a sealing resin which cures an application of visible light rays or near infrared rays thereto.
2. Description of the Related Art
In a dry battery, electricity-generating elements are accommodated in a metallic battery case, which also services as an electrode, and a metal cap which is a counter electrode. For example, as shown in FIG. 1, an alkaline battery has a metallic battery case 11 which also serves as a positive electrode terminal, and a positive electrode combining agent is filled therein. A gel-like zinc negative electrode and a negative current collector are disposed further inside the metallic battery case 11 by being separated by a separator. The negative current collector is connected to a negative electrode terminal 12. Further, the negative electrode terminal 12 is secured by a calked portion 11' of the battery case 11 with a gasket 13 placed therebetween. As can be seen from FIG. 1, the calked portion 11' of the positive electrode and the negative electrode 12 are disposed in very close proximity to each other, and if these two electrodes come into contact with each other, an external short-circuiting naturally occurs, resulting in the breakage of the electrodes and leakage of the solution.
Unless this portion is insulated and protected, not only is a coil spring-like terminal on the appliance side liable to enter between a negative electrode bottom plate and a calked portion of the positive electrode battery case at the time of fitting and using the battery, but also a short-circuiting can occur if the battery is placed upright on a metal portion with the negative electrode bottom plate placed downward during storage.
For this reason, coating and insulation are conventionally provided only by an insulating heat-shrunk sheet 15, or an insulating characteristic is secured by fitting an insulating circular or cylindrical cap (see Japanese patent Application Laid-Open No. 118855/1992). Further, there is an example in which an ultraviolet curing resin is used as an insulating and coating material (see Japanese Patent Application Publication No. 63901/1993).
If insulation is provided by coating only by the heat-shrunk sheet, there are cases where the sheet is peeled off the bottom portion of the battery due to the deterioration of an adhesive or friction during transport or storage of the battery, and the battery is liable to be subjected to damage such as the peeling off or fracture of a label by the appliance-side terminal during the fitting or detaching of the battery with respect to the appliance for which the battery is used, so that the two electrodes are liable to be exposed. Hence the battery using such an insulation lacks reliability in the insulating characteristic.
On the other hand, if the insulating circular or cylindrical cap is fitted, the reliability of insulation becomes high. However, insulating cape are products which are formed by being blanked out from an insulating sheet or by using a die assembly, and these caps are fabricated in conformity to the shapes of batteries. Since there are many shapes of batteries, it is necessary to prepare insulating caps in conformity to the shapes of the batteries, so that the inventory control of parts is troublesome. In addition, the number of steps of fitting the cape increases, so that the cost becomes high.
The method of securing the insulating characteristic by means of an ultraviolet curing resin is seen in Japanese Patent Application Laid-Open No. 63901/1993. The ultraviolet curing resin does not require the mixing of two components or heating, and can be cured in several seconds upon application of light thereto, so that the ultraviolet curing resin is an advantageous material.
However, the ultraviolet radiation is electromagnetic radiation which is harmful to the human body, and generates ozone gas, so that an ultraviolet-emitting lamp device provided with a local exhauster is required. The lamp for emitting the ultraviolet radiation is expensive.
In addition, if the ultraviolet curing resin is used as a battery insulating seal, there is a serious problem. The ultraviolet curing resin is composed of a mixture of a substance for polymerizing a radical, such as an acryl radical, and an ultraviolet initiator. The ultraviolet initiator is activated upon application of ultraviolet radiation thereto and produces a radical. That is, there is a problem in that a portion which is shaded and to which ultraviolet radiation is not applied and a thick coating portion which the ultraviolet radiation does not reach do not cure.
In a case where only the surface of the ultraviolet curing resin is cured and its interior is not cured, the resin is easily peeled off by vibrations or a stress from the outside. Further, in the interior is uncured in the case of a battery seal, the uncured resin is dispersed in and penetrates the interior of the battery, and is mixed and reacts with the electricity-generating elements, thereby undermining the performance of the battery. Therefore, such a case is not desirable.